Method of setting a focus to acquire images of a moving object and corresponding device

ABSTRACT

At least one image of a moving object is acquired using an image acquisition device equipped with an automatic focussing system. A distance between the object and the device when the effective acquisition of the image occurs is estimated based on the estimated speed and on the period of time separating a time of actuation triggering the process for acquiring the at least one image from the time of acquisition of the said effective acquisition, and the taking into account of the said distance by the automatic focussing system.

BACKGROUND

Technical Field

The present disclosure relates to the acquisition of images, and moreparticularly devices for acquiring images of at least one moving object,in particular equipped with an automatic focusing system, which may beincorporated for example into electronic devices of the tablet orcellular mobile telephone type.

Description of the Related Art

Conventionally, the focusing of image acquisition devices is based onthe analysis of images, for example using a measurement of contrast forthe majority of compact devices, or using a detection of phase fortop-of-the-range devices that often demand a high level of performancein certain situations such as for example for photographing rapidlymoving objects.

In general, the final decision on the focusing is taken by means of theanalysis of the last image being processed received by the device priorto the activation of the command for acquiring images. Despite theprogress in the techniques notably as regards the start-up and thereactivity of image acquisition devices, there still exists a time delaybetween the time of determination of the focusing and the time of theeffective acquisition of the image.

In other words, the focusing is generally always late with respect tothe effective acquisition of images, and this is all the more true whenthe objects to be photographed are moving at a high speed.

The acquisition of a sharp image of such a rapidly moving object bycompact devices or mobile telephones is therefore a real challenge.

BRIEF SUMMARY

In an embodiment, a method comprises: estimating, using an imageacquisition device, a speed of a moving object; estimating, by the imageacquisition device, a distance between the image acquisition device andthe moving object at an effective image acquisition time based on theestimated speed of the moving object and a period of time between a timeof activation of an image acquisition cycle of the image acquisitiondevice and the effective image acquisition time; setting, by the imageacquisition device, a focus of the image acquisition device based on theestimated distance; and acquiring, by the image acquisition device, animage of the moving object at the effective acquisition time using thefocus set by the image acquisition device. In an embodiment, theestimating the speed of the moving object comprises measuring distancesusing at least one time-of-flight distance sensor of the imageacquisition device. In an embodiment, the method comprises acquiring,using the image acquisition device, a plurality of images of the movingobject. In an embodiment, the method comprises: responding to a commandto auto-focus the image acquisition device by estimating a speed of amoving object. In an embodiment, setting the focus of the imageacquisition device comprises setting a position of at least one lens ofobjective optics of the image acquisition device. In an embodiment, theperiod of time is a constant.

In an embodiment, a device comprises: one or more inputs and one or moreoutputs; and circuitry, coupled to at least one of the one or moreinputs and to at least one of the one or more outputs, and which, inoperation: estimates a speed of a moving object with respect to thedevice; estimates a distance between the device and the moving object atan effective image acquisition time based on the estimated speed of themoving object and a period of time between a time of activation of animage acquisition cycle and the effective image acquisition time; andsets a focus to acquire an image of the moving object based on theestimated distance. In an embodiment, the device comprises: objectiveoptics including at least one lens, wherein circuitry sets the focus byoutputting a control signal to set a position of the at least one lens.In an embodiment, the device comprises: image acquisition circuitry,which, in one mode of operation, acquires images of moving objects; andan actuator, which, in operation, actuates an image acquisition cycle ofthe image acquisition circuitry. In an embodiment, the device comprisesat least one time-of-flight distance sensor, wherein the circuitry, inoperation, estimates the speed of the moving object based on distancesmeasured by the at least one time-of-flight sensor. In an embodiment,the circuitry, in operation, estimates the speed of the moving objectbased on distances between the moving object and the objective opticsdetermined by the at least one time-of-flight sensor at a plurality oftimes, at least one of which precedes the time of activation. In anembodiment, the at least one lens comprises a first field of view andthe at least one sensor comprises a second field of view covering atleast one third of the first field of view. In an embodiment, the atleast one sensor has a maximum range of detection, the image acquisitioncircuitry comprises a motor having a plurality of states of progressioneach corresponding to a range of focussing of the objective optics, andthe maximum range of the said at least one sensor is at least 65% of themaximum range of focussing of the objective optics. In an embodiment,the device comprises at least one of: a touch screen; and mobiletelephone circuitry.

In an embodiment, a system comprises: image acquisition circuitry,which, in operation, acquires images of objects; objective opticsincluding at least one lens; and auto-focus circuitry, which, inoperation: estimates a speed of a moving object relative to theobjective optics; estimates a distance between the objective optics andthe moving object at an effective image acquisition time based on theestimated speed of the moving object and a period of time between a timeof activation of an image acquisition cycle of the image acquisitioncircuitry and the effective image acquisition time; and sets a focus ofthe at least one lens based on the estimated distance. In an embodiment,the system comprises: at least one time-of-flight distance sensor,wherein the auto-focus circuitry, in operation, estimates the speed ofthe moving object based on distances measured by the at least onetime-of-flight sensor. In an embodiment, the circuitry, in operation,estimates the speed of the moving object based on distances between themoving object and the objective optics determined by the at least onetime-of-flight sensor at a plurality of times, at least one of whichprecedes the time of activation. In an embodiment, the system comprisesat least one of: a touch screen; and mobile telephone circuitry.

In an embodiment, a computer-readable memory medium's contents, whenexecuted by an image acquisition device, cause the image acquisitiondevice to perform a method, the method comprising: estimating a speed ofa moving object in a field of view of the image acquisition device;estimating a distance between the image acquisition device and themoving object at an effective image acquisition time based on theestimated speed of the moving object and a period of time between a timeof activation of an image acquisition cycle of the image acquisitiondevice and the effective image acquisition time; setting a focus of theimage acquisition device based on the estimated distance; and acquiringan image of the moving object at the effective acquisition time usingthe focus set by the image acquisition device. In an embodiment, theestimating the speed of the moving object comprises measuring distancesusing at least one time-of-flight distance sensor of the imageacquisition device. In an embodiment, the setting the focus of the imageacquisition device comprises setting a position of at least one lens ofobjective optics of the image acquisition device.

According to an embodiment, a method and a device are provided foracquisition of at least one image of a moving object by means of animage acquisition device equipped with an automatic focusing systemallowing the focusing of the object to be improved by means of aprediction of its positioning during the effective acquisition of theimage, and this is based on an estimation of the speed of the objectusing at least one sensor of the ToF (“Time of Flight”) type.

In an embodiment, a method is provided for acquisition of at least oneimage of a moving object by means of an image acquisition deviceequipped with an automatic focusing system. The said method comprises

an estimation of the speed of movement of the object;

a determination of the distance between the object and the device whenthe effective acquisition of the image occurs based on the estimatedspeed and on the period of time separating a time of actuation (forexample pressing a button of the photographic device or tapping an iconon the screen of a “Smart Phone”) triggering the process for acquiringthe said at least one image from the time of acquisition of the saideffective acquisition; and

the taking into account of the said distance by the automatic focusingsystem.

In an embodiment, the speed of the object may be estimated by means ofdistances obtained by at least one sensor based on the time-of-flightprinciple, commonly known by those skilled in the art under the acronym“ToF”.

In an embodiment, a device is provided for acquiring images, comprising

objective optics comprising at least one lens;

a means for acquiring images;

a triggering means able to be actuated allowing the said acquisitionmeans to be activated; and

an automatic focusing system configured for controlling the positioningof the said at least one lens.

In an embodiment, the image acquisition device furthermore comprisescontrol means comprising

estimation means configured for estimating the speed of a moving objectof which it is desired to acquire at least one image and

calculation means configured for determining, from the said estimatedspeed and from the period of time separating the time of actuation ofthe triggering means from the time of acquisition of the said at leastone image by the acquisition means, the distance between the object andthe objective optics at the said acquisition time.

The automatic focusing system is then configured for controlling theposition of the said at least one lens taking into account thisdetermined distance.

According to one embodiment, the estimation means comprise at least onesensor based on the time-of-flight principle and having a maximumdetection range.

The estimation means can be configured for estimating the speed of theobject, for example based on distances between the object and theobjective optics determined by the said at least one sensor at times atleast one of which precedes the time of actuation.

According to an embodiment, the said at least one lens comprises a firstfield of view and the said at least one sensor comprises a second fieldof view covering at least one third of the said first field of view.

According to an embodiment, the image acquisition means comprises amotor having a plurality of states of progression each corresponding toa focusing range of the objective optics, and the maximum range of thesaid at least one sensor is equal to at least 65% of the maximumfocusing range, or hyperfocal distance, of the objective optics.

In an embodiment, an electronic device is provided, for example of thetablet or cellular mobile telephone type, incorporating an imageacquisition device such as defined hereinbefore.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

One or more embodiments will now be described, purely by way ofnon-limiting example, with reference to the annexed figures, wherein:

FIG. 1 is a functional block diagram of an embodiment of an electronicdevice.

FIG. 2 is a timing diagram illustrating a focusing operation of anembodiment.

FIG. 3 illustrates a field of vision of the objective optics and a fieldof vision of a sensor of an embodiment.

FIG. 4 illustrates a distribution of states of progression of a focusingmotor in an embodiment.

DETAILED DESCRIPTION

In the ensuing description, numerous specific details are provided inorder to facilitate as much as possible understanding of the embodimentsprovided by way of example. The embodiments may be implemented with orwithout specific details, or else with other methods, components,materials, etc. In other cases, structures, materials, or operationsthat are well known are not shown or described in detail so that aspectsof the embodiments will not be obscured. Reference in the framework ofthe present description to “an embodiment” or “one embodiment” meansthat a given peculiarity, structure, or characteristic described inconnection with the embodiment is comprised in at least one embodiment.Hence, recurrence of phrases such as “in an embodiment” or “in oneembodiment” in various points of the present description does notnecessarily refer to one and the same embodiment. Moreover, thepeculiarities, structures, or characteristics may be combined in anyconvenient way in one or more embodiments.

The notations and references are here provided only for convenience ofthe reader and do not define the scope or the meaning of theembodiments.

FIG. 1 illustrates schematically an electronic device AE of the cellularmobile telephone type incorporating an image acquisition device ACIaccording to an embodiment.

The image acquisition device ACI comprises objective optics OBFincluding at least one lens L. For an improved optical performance, aplurality of different lenses may be used.

The image acquisition device ACI furthermore comprises an imageacquisition circuit or circuitry MCI, for example a matrix of pixelsassociated with a microcontroller, a triggering device MD, which, inoperation, is actuated (for example a push button or else an icon on thescreen of the camera function of a cellular mobile telephone or of atablet) allowing the said acquisition circuit MCI to be activated and anautomatic focusing system MPA configured to control the positioning ofthe said at least one lens.

The focusing system MPA may be activated continuously and/or in responseto the actuation of the triggering device MD depending on theconfiguration of the acquisition device ACI. An actuation of thetriggering device MD causes the activation of the said acquisitioncircuit MCI, and leads, in this regard, to

determining an estimated distance D between at least one object OBT, ofwhich it is desired to acquire at least one image, and the objectiveoptics OBF at the time of the effective acquisition of the image,

controlling the focusing positioning of the said at least one lens L asa function of the distance D having been determined in such a manner asto carry out the acquisition of the image of the object OBT with animproved focusing, notably when the object is moving.

The image acquisition device ACI furthermore comprises a controller MC.The controller MC comprises an estimation block or circuitry MEconfigured to estimate the speed of the moving object and a calculationblock or circuitry MCAL configured to perform a calculation ofdistances.

The blocks MC, ME and MCAL may be implemented in whole or in part assoftware modules incorporated within the microcontroller.

Furthermore, the estimation block ME comprises at least one sensor CAPbased on the time-of-flight principle and having a maximum range ofdetection.

The structure and the operation of such a sensor are well-known to thoseskilled in the art.

The sensor CAP is configured to emit a light beam towards an objectsituated within the said maximum range of detection and calculates thereturn travel time of the beam between the sensor and the said at leastone object. The “time-of-flight” of the said light beam is proportionalto the distance between the sensor and the said at least one object.

The electronic device AE may comprise one or more processors P, one ormore memories M, and discrete circuitry DC, which may be employed aloneand in various combinations to implement the functionality of theelectronic device AE. The electronic device AE also may comprise a bussystem BUS to couple various inputs and outputs of the functional blocksof the electronic device together, for example, to couple outputs of thesensor CAP to inputs of the estimation block ME, to couple outputs ofthe controller MC to inputs of the focusing system MPA, etc.

Reference is now made to FIG. 2 in order to illustrate, in more detail,the operation of the controller MC and of the estimation block ME and anacquisition of at least one image of a moving object OBJ, here a motorcar, using the image sensor device ACI equipped with the automaticfocusing system MPA.

The sensor CAP is configured to determine distances between the objectOBT and the sensor (or the objective optics OBF) at a certain frequency,for example 30 Hz, which allows the estimation block ME to estimate thedistance between the sensor and the said at least one object at variousdetection times, for example T1, T2, and to track the variation of thisdistance virtually in real time.

When, at the time of actuation T_(a), the triggering device MD isactuated so as to send an image acquisition command, the estimationblock ME is configured to estimate the speed of the object V_(OBT) fromdistances between the object OBJ and the objective optics OBF determinedby the said sensor CAP at times at least one of which precedes the timeof actuation T_(a).

By way of example, the times T2 and T_(a) will be used, however thetimes T1 and T2 could have been used.

The speed of the object V_(OBT) may then be determined using the formulabelow:

$V_{OBT} = \frac{\left( {D_{2} - D_{a}} \right)}{\left( {T_{2} - T_{a}} \right)}$

It should be noted that the speed of the object V_(OBT) corresponds tothe speed along the optical axis of the objective optics OBJ.

The calculation block MCAL is configured to determine, using the saidestimated speed V_(OBT) and the period of time separating the time ofactuation T_(a) from the time T_(c) of effective acquisition, a knownperiod since it depends on the characteristics of the device.

The distance D_(c) between the object OBT and the objective optics OBJat the said acquisition time T_(c) can therefore be determined by thecalculation block MCAL by applying the following formula:

$D_{c} = {D_{2} + {\frac{\left( {D_{2} - D_{a}} \right)}{\left( {T_{2} - T_{a}} \right)}\left( {T_{c} - T_{2}} \right)}}$

The automatic focusing system MPA controls the positioning of the saidat least one lens L taking into account the said distance D_(c) havingbeen determined.

An embodiment facilitates improving the sharpness of the acquired image,for example, when the object OBT is moving at speed.

It should be noted that the said at least one lens L comprises a firstfield of view CV1 and the said at least one sensor comprises a secondfield of view CV2, as illustrated in FIG. 3.

In order to increase the chances of success of the automatic focusing inan embodiment during the acquisition of the said at least one movingobject OBT, the second field of view CV2 may be placed in the middle ofthe first field of view CV1 (FIG. 3).

In an embodiment, the second field of view CV2 may cover at least onethird of the said first field of view CV1.

The image acquisition circuit MCI may comprise a motor MP for drivingand controlling the progression of the said at least one lens L in sucha manner as to implement the automatic focusing taking into account thesaid distance D_(c) between the object OBT and the objective optics OBFat the said acquisition time T_(c).

The said motor MP may be, for example, a mobile coil motor commonlyknown by those skilled in the art under the acronym “VCM” (for “VoiceCoil Motor”) and comprising a plurality of states of progression EA.

Each state of progression EA corresponds to a focusing range P of theobjective optics OBF. The density of distribution of the states ofprogression may not uniform as a function of the said range P. Thecloser the object to the objective optics OBF, the higher the density ofdistribution of the states of progression that may be employed (FIG. 4).

An embodiment facilitates a high level of performance of the automaticfocusing by employing a sensor with the maximum range D_(cmax) equal toat least 65% of the maximum range P_(max) of the objective optics OBF.

Some embodiments may take the form of or include computer programproducts. For example, according to one embodiment there is provided acomputer readable medium including a computer program adapted to performone or more of the methods or functions described above. The medium maybe a physical storage medium such as for example a Read Only Memory(ROM) chip, or a disk such as a Digital Versatile Disk (DVD-ROM),Compact Disk (CD-ROM), a hard disk, a memory, a network, or a portablemedia article to be read by an appropriate drive or via an appropriateconnection, including as encoded in one or more barcodes or otherrelated codes stored on one or more such computer-readable mediums andbeing readable by an appropriate reader device.

Furthermore, in some embodiments, some of the systems and/or modulesand/or circuits and/or blocks may be implemented or provided in othermanners, such as at least partially in firmware and/or hardware,including, but not limited to, one or more application-specificintegrated circuits (ASICs), digital signal processors, discretecircuitry, logic gates, standard integrated circuits, state machines,look-up tables, controllers (e.g., by executing appropriateinstructions, and including microcontrollers and/or embeddedcontrollers), field-programmable gate arrays (FPGAs), complexprogrammable logic devices (CPLDs), etc., as well as devices that employRFID technology, and various combinations thereof.

The various embodiments described above can be combined to providefurther embodiments. Aspects of the embodiments can be modified, ifnecessary to employ concepts of the various patents, applications andpublications to provide yet further embodiments.

These and other changes can be made to the embodiments in light of theabove-detailed description. In general, in the following claims, theterms used should not be construed to limit the claims to the specificembodiments disclosed in the specification and the claims, but should beconstrued to include all possible embodiments along with the full scopeof equivalents to which such claims are entitled. Accordingly, theclaims are not limited by the disclosure.

The invention claimed is:
 1. A method, comprising: measuring a pluralityof distances using at least one time-of-flight sensor of an imageacquisition device; estimating, using the image acquisition device andduring an image acquisition cycle of the image acquisition device, aspeed of a moving object based on the plurality of distances measuredusing the at least one time-of-flight sensor of the image acquisitiondevice, wherein an acquisition time of at least one of the measuredplurality of distances precedes a time of activation of the imageacquisition cycle; estimating, by the image acquisition device andduring the image acquisition cycle, a distance between the imageacquisition device and the moving object at an effective imageacquisition time based on the estimated speed of the moving object and aperiod of time between the time of activation of the image acquisitioncycle of the image acquisition device and the effective imageacquisition time; setting, by the image acquisition device and duringthe image acquisition cycle, a focus of the image acquisition devicebased on the estimated distance; and acquiring, by the image acquisitiondevice and during the image acquisition cycle, an image of the movingobject at the effective acquisition time using the focus set by theimage acquisition device.
 2. The method of claim 1, comprisingacquiring, using the image acquisition device, a plurality of images ofthe moving object.
 3. The method of claim 1, comprising: responding to acommand to auto-focus the image acquisition device by estimating a speedof a moving object.
 4. The method of claim 1 wherein the setting thefocus of the image acquisition device comprises setting a position of atleast one lens of objective optics of the image acquisition device. 5.The method of claim 1 wherein the period of time is a constant.
 6. Themethod of claim 1 wherein the image acquisition device comprisesobjective optics and a motor, the motor having a plurality of states ofprogression each corresponding to a focusing range of the objectiveoptics.
 7. The method of claim 6 wherein the at least one time-of-flightsensor has a maximum range of detection and the maximum range ofdetection of the at least one time-of-flight sensor is at least 65% of amaximum focusing range of the objective optics.
 8. A device, comprising:one or more inputs and one or more outputs; and circuitry, coupled to atleast one of the one or more inputs and to at least one of the one ormore outputs, and which, during an image acquisition cycle: estimates aspeed of a moving object with respect to the device based on a pluralityof distances measured by at least one time-of-flight sensor, wherein anacquisition time of at least one of the measured plurality of distancesprecedes a time of activation of the image acquisition cycle; estimatesa distance between the device and the moving object at an effectiveimage acquisition time based on the estimated speed of the moving objectand a period of time between the time of activation of the imageacquisition cycle and the effective image acquisition time; and controlsacquisition of an image of the moving object at the effective imageacquisition time, the controlling including setting a focus to acquirethe image of the moving object at the effective image acquisition timebased on the estimated distance.
 9. The device of claim 8, comprising:objective optics including at least one lens, wherein the circuitry setsthe focus by outputting a control signal to set a position of the atleast one lens.
 10. The device of claim 9, comprising: image acquisitioncircuitry, which, in one mode of operation, acquires images of movingobjects; and an actuator, which, in operation, actuates an imageacquisition cycle of the image acquisition circuitry.
 11. The device ofclaim 10, comprising the at least one time-of-flight sensor.
 12. Thedevice according to claim 11 wherein the at least one lens comprises afirst field of view and the at least one time-of-flight sensor comprisesa second field of view covering at least one third of the first field ofview.
 13. The device according to claim 11 wherein the image acquisitioncircuitry comprises a motor having a plurality of states of progressioneach corresponding to a focusing range of the objective optics.
 14. Thedevice of claim 13 wherein the at least one time-of-flight sensor has amaximum range of detection and the maximum range of detection of the atleast one time-of-flight sensor is at least 65% of a maximum focusingrange of the objective optics.
 15. The device of claim 8, comprising atleast one of: a touch screen; and mobile telephone circuitry.
 16. Asystem, comprising: at least one time-of-flight sensor; imageacquisition circuitry, which, in operation, acquires images of objects;objective optics including at least one lens; and auto-focus circuitry,which, in operation: measures a plurality of distances using the atleast one time-of-flight sensor; and, during an image acquisition cycle,estimates a speed of a moving object relative to the objective opticsbased on the plurality of distances measured by the at least onetime-of-flight sensor, wherein an acquisition time of at least one ofthe measured plurality of distances precedes a time of activation of theimage acquisition cycle; estimates a distance between the objectiveoptics and the moving object at an effective image acquisition timebased on the estimated speed of the moving object and a period of timebetween the time of activation of the image acquisition cycle of theimage acquisition circuitry and the effective image acquisition time;and sets a focus of the at least one lens based on the estimateddistance.
 17. The system of claim 16, comprising at least one of: atouch screen; and mobile telephone circuitry.
 18. The system of claim16, wherein the auto-focusing circuitry comprises a motor, the motorhaving a plurality of states of progression each corresponding to afocusing range of the objective optics.
 19. The system of claim 18wherein the at least one time-of-flight sensor has a maximum range ofdetection and the maximum range of detection of the at least onetime-of-flight sensor is at least 65% of a maximum focusing range of theobjective optics.
 20. A non-transitory computer-readable memory mediumcontaining contents which when executed by an image acquisition devicecause the image acquisition device to perform a method, the methodcomprising: measuring a plurality of distances using at least onetime-of-flight sensor; estimating, during an image acquisition cycle ofthe image acquisition device, a speed of a moving object in a field ofview of the image acquisition device based on the plurality of distancesmeasured by the at least one time-of-flight sensor of the imageacquisition device, wherein an acquisition time of at least one of themeasured plurality of distances precedes a time of activation of theimage acquisition cycle; estimating, during the image acquisition cycle,a distance between the image acquisition device and the moving object atan effective image acquisition time based on the estimated speed of themoving object and a period of time between the time of activation of theimage acquisition cycle of the image acquisition device and theeffective image acquisition time; setting, during the image acquisitioncycle, a focus of the image acquisition device based on the estimateddistance; and acquiring, during the image acquisition cycle, an image ofthe moving object at the effective acquisition time using the focus setby the image acquisition device.
 21. The non-transitorycomputer-readable memory medium of claim 20 wherein the setting thefocus of the image acquisition device comprises setting a position of atleast one lens of objective optics of the image acquisition device. 22.The non-transitory computer-readable memory medium of claim 21 whereinthe image acquisition device comprises a motor having a plurality ofstates of progression each corresponding to a focusing range of theobjective optics.
 23. The non-transitory computer-readable memory mediumof claim 22 wherein the at least one time-of-flight sensor has a maximumrange of detection and the maximum range of the at least onetime-of-flight sensor is at least 65% of a maximum focusing range of theobjective optics.